Sine bars



Oct. 10,1967

M. s. LIPKINS SINE BARS Filed Oct. 22, .1965

FIG. 3

United States Patent Ofiice 3,345,754 Patented Oct. 10, 1967 Filled Get. 22, 1965, Ser- No. 501,737 11 Claims. (Cl. 33 174) The present invention relates to sine bars, such as are used with standard gage blocks (as Io blocks) to set up precise reference angles.

An object of the present invention resides in features of construction of sine bars for realizing high precision without resort to exorbitant fabrication procedures.

' A further object resides in novel features of sine-bar construction facilitating setting-up of small reference angles without resort to complicatedprocedures.

An additional object relates to the provision of novel high-accuracy sine bars that are especially suitable for setting up reference angles between vertically disposed planes. These objects and others, and the novel features of sinebars pursuant to the present invention, and their advantages, will be better understood from the following detailed description of three illustrative embodiments of the broad aspects of the invention, these embodiments separately having certain specific novel features. The illustrative embodiments are described with reference to the accompanying drawings, in which:

FIGURE. 1 is a lateral elevation of a novel form of sine bar illustrating certain aspects of the invention;

FIGURE 1A is a bottom plan view of the sine bar of FIG. 1;

FIGURE 2 is a modification of the sine bar of FIGS. 1 and 1A;

FIGURE 3 is a top plan view of another novel sine bar incorporating certain additional novel features.

In FIGS. 1 and 1A, a plate 10 is made of a hard metal, preferably of an alloy that is dimensionally stable such as any of the alloys used for making standard gage blocks. The top surface and, preferably, the bottom surface of plate 10 have a bright reflecting finish, and are flatand parallel to optical standards.

A pair of spheres 12 and a third sphere 14 are in tangential contact with plate 10, and these spheres are united to plate 10 by cement 16 such as hard epoxy cement. These balls are truly spherical and have a bright finish, and they are alike in size, all within limits of optical tolerance; and they are of a hard material such as sapphire or tungsten carbide.

A ring 18 has a coincal inside surface that fits closely about each of the spheres or balls 12 and 14 and a reasonably flat face against the bottom of plate 10. This ring is held in place by epoxy cement, being cemented both to plate 10 and to its respective ball. This ring and the added cement does not disturb the tangential contact of the associated ball with plate 10, the ring and the added cement serving to strengthen the joint of the ball to the plate.

As shown in FIG. 1A, the twoballs 12 form the'base of an isoceles triangle, ball 14 being at the apex of the triangle. The altitude of the triangle L (which is also the same triangle as defined by the points of tangency of the balls against plate 10) is established by first cementing balls 12 in place and then, with a plate (not shown) of.

standardized length between balls 12 and 14, ball 14 is cemented in place. In an example, the value of L is inches, the center-to-center distance between balls 12 is 1 /2 to 2 inches, balls 12 and 14 are 4-inch in diameter, and plate is %-inch thick. The plate may be solid, or it may be deeply grooved for weight reduction except at the points of tangency of the balls.

In use the sine bar 10, 12, 14 is supported on a surface plate S and a stack of standard gage blocks G (such as Jo blocks) support ball 14 above plate S. The angle that the top surface of plate 10 makes with surface plate S is that whose sine is the height of gage blocks G divided by L. For small angles, an error of 0000005 inch of height per inch of L represents an error of one second of arc. Where L is made five inches, a one-second error of are results from an error in the gage blocks G of 0.000025 inch. A like standard of accuracy is attained in the sine bar itself, since the component parts are individually made to standards of optical accuracy and their assembly as shown involves no significant errors, or at the worst, very small and readily calibrated errors. As an overall result, the setting of angles to an accuracy of 1" of arc is readily feasible through the use of the sine bar in FIGS; 1 and 1A. For large angles, the degree of error contributed by any departure of the sine bar from the theoretical dimensions specified becomes smaller than 1". a

The sine bar of FIGS. 1 and 1A is useful as described for setting up reference angles from 0 upward, depending on the size of the stack of gage blocks G that is used. A modification is illustrated in FIG. 2, in which member 10 replaces plate 10 whose top and bottom faces are parallel. The top and bottom faces of member 10' are fiat and have the same finish as described for plate 10, but member 10 has a large angle between its top and bottom faces, e.g. This facilitates setting up large reference angles without resort to large stacks of gage blocks G. This is of advantage particularly in that the error introduced by the gage blocks is held to a minimum.

A further embodiment of the invention is illustrated in FIG. 3, including further novel features. The parts in FIG. 3 bearing the same reference numerals as in FIG. 1, but with a sufiix a, are of the same materials and are assembled in the same manner as in FIG. 1. In FIG. 3

a shim 20, whose top and bottom faces are optically flat and parallel, is interposed between each ball 12a and plate 10a, and shim 20 is joined to that plate by a peripheral coating of epoxy cement. The balls 12a are in tangential contact with shim 20, and these balls are connected by cement 16a and ring 18a to shim 20.

The sine bar represented by the parts of FIG. 3 thus far described is especially suitable for setting-upvery small reference angles. This isexplained as follows: Where gage blocks G are supplied with a minimum thickness of 0.100000 inch and where a shim 20 is made 0.100000 inch, a 0 angle is represented by using a gage block of 0.100000 inch under ball 14. Very small angles are then represented by using slightly thicker standard gage blocks under ball 14a. Of course, the same effect can be realized using a pair of gage blocks 0.100000 thick,

under balls 12 in FIG. 1; but this would require additional a distinct advantage.

As mentioned above, FIG. 3 is a plan view. The top surface of plate 10a is vertical in the use illustrated. The bottom edge is fiat and rests on an optically flat surface. In place of the surface plate S of FIG. 1, which is no part of the sine bar, a plate 22 is included as part of the sine bar, having optically true, flat parallel opposite surfaces, including surface S against which balls 12a and gage blocks G rest. A flat-faced block 24 as of tungsten carbide is fixed to plate 22. A longitudinal edge of plate 22 at right angles to surface S is flat and coplanar with the above described edge of plate 10a which rests on the optically flat surface. Plate 22 may be hard, as of tungsten carbide; or an insert 22' of tungsten carbide can be used to support balls 12a. The surface of insert 22' is coplanar with the top surface 8' against which gage blocks G are assembled. The top edges of plates 10a and 22 are flat and parallel to the bottom edges so that the assembly can be turned over, as may be needed.

Spring 26 is tensioned between a fastening point 28 on plate 113a adjacent the balls 12a, and another fastening point 30 on plate 22 adjacent the supporting area for gage blocks G opposite ball 14a. Two such springs 26 flanking blocks G can be used where large angles are to be set up and where, consequently, blocks G would approach more closely to block 24. Spring or springs 26 bias balls 12a against bot-h block 24. and plate 22, and also bias ball 14a against gage blocks G. The location of the spring biasing means as shown has the advantage of avoiding stresses in plates a and 22 at other locations (as midway between ball 14a and 12a) where warping stresses could develop in those plates and Where rapidly rising spring tension could develop as the stack of blocks G becomes large.

It will be recognized that the features of FIG. 1 are utilized in FIG. 3, the latter affording verticalplane reference angles, often needed as on an optical bench. In more general application, shim may be omitted from FIG. 3, the sine bar of FIG. 3 then appearing exactly as is shown in FIG. 1. In all the figures, the inclusion of complete balls, cemented in place so as to be tangent to another accurately oriented flat surface is a feature that promotes a high order of accuracy in the resulting sine bar. Further, the use of cement in lieu of screws or comparable mechanical fastening means avoids any small mechanical deformation that would result from tightening of any mechanical fasteners. Additionally, where cement is used, it can be removed with appropriate softeners (even in the case of epoXy cement) and the balls can be rotated in case wear of the balls makes this adjustment worthwhile.

The foregoing description of a few forms of sine bar incorporating features of the invention will suggest variations and varied applications of the novel features to those skilled in the art. Consequently, the invention should be broadly construed in a manner consistent with the spirit and scope of the invention.

What is claimed is:

1. A sine bar for use with a companion flat surface plate and gage blocks for establishing precise angles between the surface plate and the top of the sine bar, said sine bar including a member having true top and bottom fiat accurately related faces, and three hard spheres of equal diameter in tangential contact with one of said fiat faces and united thereto by cement in a triangular pattern, two of said spheres being spaced apart and the centers of the two spheres defining a base line of the triangular pattern, and the third of said spheres being spaced sub stantially from both of said two spheres, the distance between the center of the third sphere and the base line constituting an accurately established altitude of the triangular pattern to be used in calculations of angles between said top face and the surface plate.

2. A sine bar in accordance with claim 1, further including a ring surrounding each said sphere and joined by cement both to the respective sphere and to said memher.

3. A sine bar including a rigid member having true top and bottom flat faces, three hard spheres of equal diameter arranged in a triangle at one of said faces including a pair of said spheres near one end of one of said flaf faces and the third of said spheres near the opposite end of said one flat face, and shim means secured to said one face and having accurately flat and parallel op- 41 posite faces, said shim means being interposed between said one flat face and at least one of said spheres, said spheres being in tangential contact with said shim means and with said one flat face, respectively, and united thereto by cement.

4. A sine bar including a first rigid member having a flat reference face and having fiat mounting areas for spheres, three hard spheres united by cement to said flat mounting areas and in tangential contact therewith, a pair of said spheres being of equal diameter and disposed adjacent to one end of one of said members, the third sphere being mounted adjacent the opposite end of said member, a second rigid member having flat and parallel opposite faces and having a vertical step part united to one of said faces and spaced away from one end thereof, said pair of spheres being in tangential contact with said second member and with said step part, and resilient means extending from one of said members to the other for holding said pair of spheres in tangential contact as aforesaid.

5. A sine bar in accordance with claim 4 wherein all of said spheres are in tangential contact with coplanar fiat surfaces of said first rigid member and are secured thereto directly by cement.

6. A sine bar in accordance with claim 4 wherein a shim is interposed between said pair of spheres and said first member.

'7. A sine bar in accordance with claim 4 wherein a lateral face of said first member is flat and perpendicular to said flat reference face of said first member, and wherein said second member has a fiat lateral surface perpendicular to the fiat faces of said second members and coplanar with the lateral surface of said first member.

8. A sine bar in accordance with claim 4, said spheres of said first member confronting respective portions of said second member, said resilient means consisting essentially of a tension spring having one end secured to said first member adjacent to a sphere thereon, the other end of the spring being secured to said second member at a relatively remote point adjacent to the portion thereof confronted by one of said spheres.

9. A sine bar in accordance with claim 4, including at each sphere a ring encircling the sphere and joined by cement to both the sphere and the related mounting area of the rigid member.

10. A sine bar in accordance with claim 1, wherein said top and bottom flat faces are parallel.

11. A sine bar in accordance with claim 3, wherein sid pair of spheres are spaced equally from said member by said shim means.

References Cited UNITED STATES PATENTS 2,306,227 12/1942 Seidel 33 174 2,429,517 10/1947 Knapp 33 174 2,472,306 6/1949 Minuto 33 174 2,494,715 1/1950 Mathews 33 174 2,567,517 9/1951 Keebler s3 174 2,609,612 9/1952 M1111 33 174 2,828,589 4/1958 Hercik 33-174 3,243,885 4/1966 Johnson 33 -174 OTHER REFERENCES Article by H. BoehlyAmerican MachinistFeb. 1, 1933, pages and 91.

SAMUEL S. MATTHEWS, Primary Examiner. 

1. A SINE BAR FOR USE WITH A COMPANION FLAT SURFACE PLATE AND GAGE BLOCKS FOR ESTABLISHING PRECISE ANGLES BETWEEN THE SURFACE PLATE AND THE TOP OF THE SINE BAR, SAID SINE BAR INCLUDING A MEMBER HAVING TRUE TOP AND BOTTOM FLAT ACCURATELY RELATED FACES, AND THREE HARD SPHERES OF EQUAL DIAMETER IN TANGENTIAL CONTACT WITH ONE OF SAID FLAT FACES AND UNITED THERETO BY CEMENT IN A TRIANGULAR PATTERN, TWO OF SAID SPHERES BEING SPACED APART AND THE CENTERS OF THE TWO SPHERES DEFINING A BASE LINE OF THE TRIANGULAR PATTERN, AND THE THIRD OF SAID SPHERES BEING SPACED SUBSTANTIALLY FROM BOTH OF SAID TWO SPHERES, THE DISTANCE BETWEEN THE CENTER OF THE THIRD SPHERE AND THE BASE LINE CONSTITUTING AN ACCURATELY ESTABLISHED ALTITUDE OF THE TRIANGULAR PATTERN TO BE USED IN CALCULATIONS OF ANGLES BETWEEN SAID TOP FACE AND THE SURFACE PLATE. 